<template>
  <div class="q-pa-md">
    <t-table
      class="my-sticky-dynamic"
      flat
      bordered
      title="Treats"
      :rows="rows"
      :columns="columns"
      :loading="loading"
      row-key="index"
      virtual-scroll
      :virtual-scroll-item-size="48"
      :virtual-scroll-sticky-size-start="48"
      :pagination="pagination"
      :rows-per-page-options="[0]"
      @virtual-scroll="onScroll"
    />
  </div>
</template>

<script>
  import { computed, nextTick, ref } from 'vue';

  const columns = [
    {
      name: 'index',
      label: '#',
      field: 'index',
    },
    {
      name: 'name',
      required: true,
      label: 'Dessert (100g serving)',
      align: 'left',
      field: row => row.name,
      format: val => val,
      sortable: true,
    },
    {
      name: 'calories',
      align: 'center',
      label: 'Calories',
      field: 'calories',
      sortable: true,
    },
    { name: 'fat', label: 'Fat (g)', field: 'fat', sortable: true },
    { name: 'carbs', label: 'Carbs (g)', field: 'carbs' },
    { name: 'protein', label: 'Protein (g)', field: 'protein' },
    { name: 'sodium', label: 'Sodium (mg)', field: 'sodium' },
    {
      name: 'calcium',
      label: 'Calcium (%)',
      field: 'calcium',
      sortable: true,
      sort: (a, b) => parseInt(a, 10) - parseInt(b, 10),
    },
    {
      name: 'iron',
      label: 'Iron (%)',
      field: 'iron',
      sortable: true,
      sort: (a, b) => parseInt(a, 10) - parseInt(b, 10),
    },
  ];

  const seed = [
    {
      name: 'Frozen Yogurt',
      calories: 159,
      fat: 6.0,
      carbs: 24,
      protein: 4.0,
      sodium: 87,
      calcium: '14%',
      iron: '1%',
    },
    {
      name: 'Ice cream sandwich',
      calories: 237,
      fat: 9.0,
      carbs: 37,
      protein: 4.3,
      sodium: 129,
      calcium: '8%',
      iron: '1%',
    },
    {
      name: 'Eclair',
      calories: 262,
      fat: 16.0,
      carbs: 23,
      protein: 6.0,
      sodium: 337,
      calcium: '6%',
      iron: '7%',
    },
    {
      name: 'Cupcake',
      calories: 305,
      fat: 3.7,
      carbs: 67,
      protein: 4.3,
      sodium: 413,
      calcium: '3%',
      iron: '8%',
    },
    {
      name: 'Gingerbread',
      calories: 356,
      fat: 16.0,
      carbs: 49,
      protein: 3.9,
      sodium: 327,
      calcium: '7%',
      iron: '16%',
    },
    {
      name: 'Jelly bean',
      calories: 375,
      fat: 0.0,
      carbs: 94,
      protein: 0.0,
      sodium: 50,
      calcium: '0%',
      iron: '0%',
    },
    {
      name: 'Lollipop',
      calories: 392,
      fat: 0.2,
      carbs: 98,
      protein: 0,
      sodium: 38,
      calcium: '0%',
      iron: '2%',
    },
    {
      name: 'Honeycomb',
      calories: 408,
      fat: 3.2,
      carbs: 87,
      protein: 6.5,
      sodium: 562,
      calcium: '0%',
      iron: '45%',
    },
    {
      name: 'Donut',
      calories: 452,
      fat: 25.0,
      carbs: 51,
      protein: 4.9,
      sodium: 326,
      calcium: '2%',
      iron: '22%',
    },
    {
      name: 'KitKat',
      calories: 518,
      fat: 26.0,
      carbs: 65,
      protein: 7,
      sodium: 54,
      calcium: '12%',
      iron: '6%',
    },
  ];

  // we generate lots of rows here
  let allRows = [];
  for (let i = 0; i < 1000; i++) {
    allRows = allRows.concat(seed.slice(0).map(r => ({ ...r })));
  }
  allRows.forEach((row, index) => {
    row.index = index;
  });

  const pageSize = 50;
  const lastPage = Math.ceil(allRows.length / pageSize);

  export default {
    setup() {
      const nextPage = ref(2);
      const loading = ref(false);

      const rows = computed(() =>
        allRows.slice(0, pageSize * (nextPage.value - 1)),
      );

      return {
        columns,
        rows,

        nextPage,
        loading,

        pagination: { rowsPerPage: 0 },

        onScroll({ to, ref }) {
          const lastIndex = rows.value.length - 1;

          if (
            loading.value !== true &&
            nextPage.value < lastPage &&
            to === lastIndex
          ) {
            loading.value = true;

            setTimeout(() => {
              nextPage.value++;
              nextTick(() => {
                ref.refresh();
                loading.value = false;
              });
            }, 500);
          }
        },
      };
    },
  };
</script>

<style lang="sass">
  .my-sticky-dynamic
    /* height or max-height is important */
    height: 410px

    .q-table__top,
    .q-table__bottom,
    thead tr:first-child th /* bg color is important for th; just specify one */
      background-color: #00b4ff

    thead tr th
      position: sticky
      z-index: 1
    /* this will be the loading indicator */
    thead tr:last-child th
      /* height of all previous header rows */
      top: 48px
    thead tr:first-child th
      top: 0

    /* prevent scrolling behind sticky top row on focus */
    tbody
      /* height of all previous header rows */
      scroll-margin-top: 48px
</style>
